Liquid coaxial line and rotary joint



March 11, 1952 J. VIOLETTE 2,588,436

LIQUID COAXIAL LINE AND ROTARY JOINT Filed 001:. 25, 1945 3 Sheets-Sheet1 RICHARD J. VIOLETTE March 1952 R. J. VIOLETTE LIQUID COAXIAL LINE ANDROTARY JOINT Filed Oct. 25, 1945 3 Sheets-Sheet 2 riff EHWVMAAAAAMW Aall RICHARD J. VIOLETTE March 11', 1952 R. J. VIOLETTE LIQUID COAXIALLINE AND ROTARY JOINT 3 Sheets-Sheet 3 Filed 001;. 25, 1945 gwuem/bobRICHARD J. VIOLETTE Patented Mar. 11, 1952 UNITED STATES PATENT OFFICELIQUID COAXIAL LINE AND ROTARY JOINT Richard J. Violette, Washington, D.0. Application October 25, 1945, Serial No. 624,617

(Granted under the act of March 3, 1883, as amended April 30, 1928; 3'700. G. 757) 4 Claims.

This invention relates to high frequency transmission lines and, moreparticularly, to such lines of the concentric type having a swing jointand suitable for use for radio frequency energy at high frequencies andabove.

One object of the present invention is the use of an organo-siliconpolymer fluid as a dielectric medium for insulating one or more innerconductors within the outer tubular line member of a concentrictransmission line system.

Another object of the invention is to provide such a transmission linein which the concentric conductors in one part may freely swivel orrotate relative to the cooperating concentric conductors of therelatively stationary part of the system, permitting correspondingmovement of the coupled conductor sections, but in which such membersare constantly retained in fluid-tight and leak-proof joint-formingrelation.

A further object of the invention is to provide a transmission line ofthe above class having. the above advantages and which at the same timeincludes compensating means whereby expansion and contraction of theliquid dielectric within the line may occur due to temperaturevariations incident to its operating nvironment without injury ordisplacement of the concentric conductors of the transmission linesystem.

These and other objects of the invention will be best understood. andappreciated from the following description of a particular embodimentthereof, for purposes of illustration only, and shown in theaccompanying drawings, in which:

Fig. 1 is a side elevation of the concentric transmission line inaccordance with the present invention as adapted for use with highfrequency radio equipment;

Fig. 2 shows an enlarged longitudinal section, in part, of thetransmission line shown in Fig. 1;

Fig. 3 is an enlarged cross-sectional View taken substantially acrossthe section-line 3-3 of Fig. 1;

Fig. 4 is an enlarged longitudinal section, in part, of the innerconductor sub-assembly showing the middle and central conductorsemployed in the transmission line system of Fig. 1.; and

Figs. 5 and 6 are end views of the fluted insulator spacers employed forsupporting the middle and central conductors, respectively.

Shipboard installation of concentric feeders and transmission linesgenerally associated withhigh frequency equipment including theirantenna systems often are mounted at locations where they are requiredto operate at high temperatures, such as is encountered by leads andfeeders to antennas mounted back of smoke stacks aboard ships. Ifconcentric leads and feeders of the solid dielectric type, i. e., inwhich the inner conductor is surrounded with a solid insulating materialsuch as polyethylene, are installed in such locations the hightemperatures normally encountered in the vicinity of the stack, whichoften run above 300 F., are sufficient to produce a considerable changein length of the solid dielectric material within such cables withconsequent fracture or rupture thereof. This expansion of the soliddielectric medium also has a serious disturbing effect in that arc-oversoften are experienced at the locations of fracture when the contractionof the solid dielectric material takes place as well as the formation ofcarbon traces which destroy the subsequent insulating protectionafforded by the affected dielectric medium.

In the high frequency concentric line according to the present inventionsilicone polymer fluid such as disclosed in the Patent 2,377,689, issuedJune 5, 1945, to Hyde, which has a high dielectric property suitablethrough ranges of cured to the coupling fitting at the end of the feederrun and provides an expansion chamber for the overflow or axialdisplacement of the fluid dielectric which fills the rotating unit.

Referring now to Fig. 1 in detail, there is shown a concentric rotaryjoint transmission line in accordance with the present invention that isparticularly adapted for use with a liquid dielectric. The line systemcomprises a length of concentric line generally designated 10 having anouter conductor l2 and a middle or intermediate conductor l3, both beingtubular and formed of brass, copper or other good. conducting material;and a central conductor or metal rod l4 which is coaxial with theconductors l2 and 43 supported in this position by suitable dielectricspacersor beads (not shown) within the middle conductor l3. The lowerend of the outer tubular conductor I2 is terminated in a T-pi-pe fitting15 which carries a coaxial tuning ductors of a coaxial cable (not shown)are con-'" nected to the middle tubular conductor l3 and the outertubular conductor I2, respectively, of

the guide iii.

The upper end of the guide 15 is terminated in a hollow cross-pipefitting 20 formed with four 90 tubular pipe-connector stubs 2!, 22, 23and" 24, respectively, the pipe stub 2| being suitably aifixed to theupper end of the outer tubular conductor i2, as by soldering orotherwise. The cross-pipe 23 mounts on its pipe stubs 22 and 24 thecoaxial tuning stub 25 and the concentric stufiing tube 23 respectively,both of which are positioned at right angles to the main guide line H],while on the pipe stub 23 there is positioned in axial coincidence withthe axis of the guide in an expansion compensator device generallydesignated 28 which forms one important feature of the present inventionand whose detailed construction and operation will be hereinafterdescribed.

As shown in greater detail in Fig. 2, the concentric tubular conductorsl2 and i3 and the central rod Hi of the guide w are connected respec-.tively through appropriate resiliently fingered contact sleeves 3!, 35aand 3!!) respectively of a coaxial swing joint 39, which will bedescribed hereinafter in somewhat greater detail, to the correspondingtubular conductors 32 and 33 and the central rod 34 of the upper ormovable portion of the line system. The conductors 32, 33 and 34, asthus joined together form rotatable axial extensions of thecorresponding stationary conductors I2, I3 and M. The middle tubularconductor 33 and the central rod 34 project into the interior of thecross-pipe and make substantially a right angle connection with themiddle tubular conductor 35 and the central rod 36, respectively,positioned coaxially of the tuning stub 25. Also the middle tubularconductor 33 and the outer tubular conductor 32 of the rotary part ofthe guide system is connected respectively to the inner conductor 38 andthe'other metallic braided conductor 33 of the cable 43 by means ofwhich the output from one of the antennas (not shown) is fed to thecoaxial pair of conductors 32, 33 and, in turn, through the rotary jointto coaxial conductors l2, [3 of the line system. To this end, the middletubular conductor 33 is connected by means of metallic insert 4| andresilient contact sleeve 42 to the inner conductor 38 of the cable Ml,while the outer tubular conductor 32 is connected through pipe stubs 2!and 24, metallic housing 33 and associated coupling insert M and lockdevice 45 to the outer metallic braid 39 of the cable All.

The tuning stubs H and are similar in con- (not shown) to an externalcircuit device such as, for example, a receiver and/or an indicatoroutside the pedestal mount supporting the line system. I

Referring to Fig. 1 again, there is shown a rotary or swing joint 33 ofthe concentric type which is positioned in the main run of the guide [0intermediate the cross-pipe 25 and the T-pipe l5, this swing joint beingof a known construction in the electrical art adapted for enablingrotational movement of. the conductors 32, 33 and 34 carried by theupper portion of the guide system affixed to the cross-pipe 23 withrespect to the corresponding stationary part of these concentricconductors enclosed within and forming the guide l0. One type swingjoint of the aforementioned character which has been found satisfactoryfor this purpose is the so-called Chiksan rotary joint for electricalconnectors manufactured by the Chiksan Tool Company, Brea, California.More specifically, there is disclosed in Patent No. 2,369,849 to DwightM. Phillips, granted February 20, 1945, a rotary joint of this generalcharacter designed for use with tubular electrical conductors of aconcentric line system.

Briefly described, the Chiksan swing joint employs a ball bearing rotaryportion 48 to which is suitably attached the movable concentricconductor selections 32, 33 and 34 for providing rotary or swivelconnection thereof to the corresponding stationary conductors l2, l3 andH of the guide 13, as shown in Fig. 2. The cylindrical stationaryportion 49 of the swing joint 30 carries a circular flange 39 by meansof which the joint and guide system may be attached to suitable supportsuch as, for example, the antenna pedestal.

The transmission line system H] including the joint 30 and a part of thetuning stubs I! and 25 is filled with a silicone polymer fluid, one typeof which is manufactured by the Dow-Corning Company. The silicone fluidpreferably is an organo-compound of silicon in which the skeleton of thecompound is an oxygen chain having organic radicals directly connectedto the silicon atoms. The fluid is characterized further by having asubstantially flat viscosity curve, high dielectric capacity, andthermal stability.

In order to prevent the silicone oil from leaking out of the line Itsuitable seals 50 and BI are provided in the tuning stub 25 and stuffingtube 26 respectively, such seals being preferably of rings of live gumrubber mounted within a suitable clamping device, as is shown in Fig. 2.Similarly, the tuning stub l1 and the stuffing tube l8 each are providedwith the above-described sealing arrangements.

In order that the silicone oil can insulate the middle tubularconductors I3, 33 and 35 from struction, and both are connected to thesame their respective central rods i l, at and 36, suitable holes 53 areprovided in the side walls of these middle conductors, see Fig. 4, sothat the silicone oil in the cylindrical space surrounding these middleconductors and their respective enclosing outer tubular conductors canflow inside the middle conductors around the central rods l4, 34 and 33respectively. The polyethylene spacers-' 55 and 53, see Figs. 4, 5 and6, for insulatingly supporting for the middle tubular conductors andtheir central rods, respectively, are shown as comprising annular discmembers having a plurality of longitudinal partially circular flutes atspaced intervals in their outer peripheries to permit the silicone oilto flow freely axially along the major portion of the full length ofline system including the-swing joint in filling. Sincethe silicone oilor fluid has high dielectric constant it effectively insulates theinsulator spacers 5'5 and 5,6. and their associated conductors.

In Fig. 2 there is shown in sectional elevation details of the expansioncompensator device 28 which comprises a hollow cylindrical can at openat its bottom end and closed at its top end, as at 6 l, the bottom openend portion of the can tightly fitting over and being attached by screws62 to the annular closure member 63 which in turn is sweated onto orotherwise united in a fluid-tight fashion to the outer end portion ofthe pipe stub 23. Provided in the upper face of the closure disc 63 isan annular reentrant groove 64 which receives and anchors one end of theflexible expansible metal bellows 65. The other end of this bellows isprovided with a metal lid 66 having a centrally apertured insert Elclosed by a bleeder plug 68 which has screw threaded connectiontherewith. It will be evident from the foregoing description that anylongitudinal displacement or'floW of the silicone fiuid from the linesystem into the interior of the bellows. 65 as would occur inresponse-to the expansion of the fluid due to the high temperaturesnormally existing in the vicinity" of its installed location will befollowed by appropriate expansion of the bellows 65 and thus compensatefor this change in volume of the liquid dielectric.

As thus constructed it will be seen that the transmission line providedis one which may be readily assembled and disassembled and that it, atthe same time, isadapted to accommodate for any volume changes incidentto expansion and contraction of the dielectric fluid which may occur dueto temperature and weather variations without any likelihood of bucklingor other injury to the line components. The middle and centralconductors also are sufficiently insulated from the outer conductors towithstand any high voltage which it may be desired to transmit throughthe line yet a the same time permitting rotational movement of the upperpart of the line, as desired.

In one practical application of the invention the main part of the lineincluding the rotary joint under electrical tests showed a corona onsetat 30,000 volts.

While various metal combinations may be employed to provide springcontact at the friction surfaces of the concentric sleeve membersforming the rotary joint 30 it was found that certain metal combinationswhen used with Dow-Corning silicone fluid #200 (polymethyl siloxane orpolymerized methyl silicone) as a lubricant and a dielectric material inthe rotary joint assembly, wore excessively with noticeable flaking andmetallic particle sludge contamination. The preferred metal combinationshowing minimum wear and contamination effect in Dow-Corning #200silicone fluid was found to be silver tipped fingers on the sleeves 3!,3| a and Nb respectively, spring contact of the silver fingers beingeffected at a friction surface on hardened steel. This silversteelrotary frictional combination showed no noticeable sludge at 200,000revolutions at 100 R. P. M., and the silver fingers of the rotary partstaking on a slight polish after 500,000 revolutions.

It will now be clear from the foregoing description that a thoroughlypractical and durable liquid rotary coaxial joint and transmission lineconstruction has been provided which is capable of operating efiicientlyand in which the several objects hereinabove mentioned, as well as manyothers now apparent are accomplished.

As many changes could be made in the above: construction and manyapparently different em bodiments of this invention could be madewith-:.

out departing from the scope thereof, it is to be understood that allmatter hereinabove set forth in the above description or shown in theaccomanying drawings, shall be interpreted as illustrative and not in alimiting sense, and that no limitations upon this invention areintendedv other than are imposed by the scope of the appended claims.

The invention described herein may be manu' joint including outer,intermediate, and central concentric fingered sleeve membersrespectively interconnecting the outer, intermediate, and centralconductor of each end of said line and adapted to permit relativerotation of the corresponding line conductors at either side of saidjoint while maintaining the electrical continuityof said outer,intermediate and central conductors throughout the length of said line,the rotary joint and associated concentric lines being filled with aliquid polymerized silicone to provide a lubricant for the joint and adielectric for the line, the fingered portions of said sleeves being ofsilver and having frictional engagement with hardened steel contactsurfaces on said con ductors, and means for compensating for expansionof said liquid when subjected to temperature ranges from -60 F. to +300F., said compensating means comprising an adjustable bellows at one endof said line and responsive to the axial how of the displaced liquidtherein incurred by being subjected to such variable temperatureconditions.

2. In combination, a rotary joint including outer and inner concentricfingered sleeve members, and a concentric transmission line havingsections at either side of said rotary joint and coaxial therewith, eachof said line sections comprising an outer metallic tubular conductor andan inner metallic conductor, the outer fingered sleeve member havingtelescopic frictional connection with the adjacent end portions of theouter conductors of each line section establishing electrical connectiontherebetween for rotaticnal motion, the inner fingered sleeve memberhaving telescopic frictional connection with the adjacent end portionsof the inner conductors of said line sections to maintain electricalconnection between said inner conductors for rotational motion, therotary joint and associated concentric lines being filled with a liquidpolymerized silicone to provide a lubricant for the joint and adielectric for the concentric lines, the fingered contact portions ofsaid sleeves being of silver and having frictional engagement withhardened steel contact surfaces on said respective outer and innerconductors.

3. A high frequency transmission line comprising an inner and an outertubular metallic conductor and a central metallic rod all concentricallyarranged with respect to each other, a concentric rotary joint locatedintermediate the ends of said line in the main run thereof andcontaining rotary connectors for said outer and inner tubular conductorsand said central rod, a hollow junction fitting at one end of said line,said junction fitting being of conducting material and having aplurality of tubular pipe stubs thereon, a concentric tuning stub havinginner and outer tubular metallic conductors and a central rod, the outertube of said tuning stub being secured to one of said pipe stubs and theinner conductors of said tuning stub being connected within saidjunction fitting to the intermediate and central conductors respectivelyof body portion of said line, means for connecting the outer conductorof a two-conductor cable to another of said pipe stubs of the junctionfitting, means within said junction fitting for connecting the innerconductor of the aforementioned twoconductor cable to the intermediateconductor of the body portion of said transmission line, a liquiddielectric medium surrounding the intermediate and central conductors ofsaid line, and means for compensating for expansion and longitudinaldisplacement of said dielectric liquid when it is subjected totemperature ranges from 60 F. to +300 F., said compensating means beingmounted on the third pipe stub member of said junction fitting andcomprising an adjustable metallic bellows in communication with theinterior of said hollow junction fitting and arranged for flow of thedisplaced dielectric liquid therein as will occur when said dielectricliquid is subjected to the aforesaid variable temperature conditions.

4. In combination, a rotary joint including outer and inner concentricfingered sleeve members, and a concentric transmission line havingsections at either side of said rotary joint and coaxial therewith, eachof said line sections comprising an outer metallic tubular conductor andan inner metallic conductor, the outer fingered sleeve memben havingtelescopic frictional connection with the adjacent end portions of theouter conductors of each line section establishing electrical connectiontherebetween for rotational motion, the inner fingered sleeve memberhaving telescopic frictional connection with the adjacent end portionsof the inner conductors of said line sections to maintain electricalconnection between said inner conductors for rotational motion, therotary joint and associated concentric lines being filled with a liquidpolymerized methyl silicone to provide a lubricant for the joint and adielectric for the concentric lines, the fingered contact portions ofsaid sleeves being of silver and having frictional engagement withhardened steel contact surfaces on said respective outer and innerconductors.

RICHARD J. VIOLETTE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,854,255 Green Apr. 19, 19321,879,746 Holden Sept. 27, 1932 1,892,663 Del Mar Jan. 3, 1933 1,912,794Peterson June 6, 1933 1,923,147 Hirshfeld Aug. 22, 1933 2,047,000Calvert July 7, 1936 2,345,019 Van Alstyne Mar. 28, 1944 2,377,689 HydeJune 5, 1945 2,452,144 Phillips Oct. 26, 1948

